1. Field of the Invention
This invention relates generally to an apparatus for accumulating charged particles and, more particularly, to a charged particle accumulator used as, for example, a light source for producing synchrotron radiation light.
2. Description of the Related Art
FIG. 1 schematically shows the construction of a conventional charged particle accumulator, such as the one described on p. 22 of TELL-TERAS ACTIVITY REPORT (1980-1986), which has a vacuum vessel 1 in the form of a ring, deflecting electromagnets 2, quadrupole electromagnets 3, a low speed pulse electromagnet 4, a high speed pulse electromagnet 5 and a high frequency cavity 6. These components constitute an accumulating ring. High speed electrons are generated by a linear electron accelerator 7.
FIG. 2 shows a locus of a charged particle in a phase plane at the outlet of the low speed pulse electromagnet 4. In FIG. 2, the abscissa represents the deviation from the central orbital path and the ordinate represents the inclination of the charged particle beam from the center axis. A point 8 represents the position of an incident charged particle at the outlet of the low speed pulse electromagnet 4. A point 9 designates the state of the incident charged particle at the position of the high speed pulse electromagnet 5. A point 10 designates the state of the incident charged particle after the same has passed through the pulse electromagnet 5. A point 11 designates the state of the incident charged particle when the same returns to the position of the low speed pulse electromagnet 4. A point 12 represents the position of the incident particle when the same completes one revolution through the accumulating ring. Points 13 and 17 represent the positions of accumulated charged particles. A wall 18 represents a side wall of the low speed pulse electromagnet 4.
The conventional charged particle accumulator is thus constructed as explained above. The motion of charged particles at the time of introduction will be explained below. The path for electrons generated by the linear electron accelerator 7 is deflected by the low speed pulse electromagnet 4 so that each electron enters into a state such as that represented by the point 8 in FIG. 2. When the electron comes to the high speed pulse electromagnet 5, the position of the electron in the phase plane is as represented by the point 9. At this time, the inclination of the electron is changed in a step manner by the vertical magnetic field produced by the high speed pulse electromagnet 5 so that the state of the electron is changed to that represented by the point 10. When the electron thereafter comes to the low speed pulse electromagnet 4 again, the position of the electron is at the point 11., When the electron thereafter comes to the low speed pulse electromagnet 4 by undergoing the above-described effect over again, the position of the electron is at the point 12. The electron moves in the phase plane by repeating this cycle. If the electron does not collide against the side wall 18 until the magnetic field of the high speed pulse electromagnet 5 is extinguished, the electron introduced from the outside is considered to be stored in the accumulator. On the other hand, the positions of other electrons already stored move successively from the point 13 to the point 17 as they undergo the same effect.
This process will be explained below in more detail. The pulse electromagnet 5 produces, in the orbital path for the charged particle beam, a magnetic field in the vertical direction alone to deflect the charged particle beam path to a certain extent. The need for the pulse electromagnet 5 is based on the following reason. In a case where only a magnetic field constant with respect to time acts on the beam, the beam proceeds along a line such as that represented by the circular arc concentric with the center axis of the phase plane of FIG. 2. That is, the beam proceeds along the circular arc passing through the point 8 as indicated by the broken line in FIG. 2, and thereafter returns to the position of the point 8. In this case, however, the beam cannot be introduced because it collides against the side wall 18 of the low speed pulse electromagnet 4. To maintain the introduced beam inside the accumulator, it is necessary to deflect for only a certain period of time the orbital path for the beam by the pulse electromagnet 5. If the current for the pulse electromagnet 5 is shut off, for example, after the introduced beam has been changed to the position of the point 10, the beam thereafter proceeds in accordance with the circular arc concentric with the center axis of FIG. 2, as indicated by the broken line passing through the point 10. Thus, the introduced beam traces the orbital path located inside the first position in FIG. 2 and does not deviate outwardly from this path.
This conventional charged particle accumulator entails various problems which reside in that
1) the orbital paths for stored charged particles are disturbed because the high speed pulse electromagnet 5 uniformly produces the vertical magnetic field;
2) the capacity of the power source for the high speed pulse electromagnet is large because the space to be filled with the produced magnetic field is large;
3) The next charged particles to be stored cannot be introduced until the changed orbital paths for the stored charged particles are restored;
4) for this reason, the accumulator cannot be used as a synchrotron radiation light source during introduction;
5) introduced charged particles collide against the side wall of the low speed pulse electromagnet unless the pulse width for the high speed pulse electromagnet is sufficiently small;
6) a further increase in the power source capacity is therefore required; and
7) introduced charged particles pass through a point at a large distance from the central orbital path, and it is necessary to increase the effective range of the magnetic field of each of the deflection electromagnet and the quadrupole electromagnet of the accumulating ring.